A general object of the present invention is to reduce or solve the aforementioned problems of the prior art by providing a type of backlight device characterized by the fact that it is free of the influence of the offset voltage of the differential amplifier.
This and other objects and features are provided, in accordance with an aspect of by a backlight device having an LED circuit, a driving transistor and a current detector; when said driving transistor is turned ON by the output signal of said amplifier, current flows in said LED circuit, said driving transistor, and said current detector; the detection voltage generated by said current detector according to said current and a reference voltage are input to said amplifier, and said driving transistor utilizes said amplifier to perform control such that the voltage differential between said detection voltage and said reference voltage is reduced; said amplifier comprises a first input transistor and a second input transistor whose source terminals are connected to each other, a load circuit connected to the drain terminals of said first input transistor and second input transistor, an input exchange circuit that inputs said detection voltage to the gate terminal of at least one input transistor among said first input transistor and second input transistor, and inputs said reference voltage to at least the other input transistor, and an exchange controller, which is connected to said input exchange circuit, controls said input exchange circuit, causes said detection voltage to be input to the input transistor having said reference voltage input to it among said first input transistor and said second input transistor, and causes said reference voltage to be input to the input transistor having said detection voltage input to it.
According to an aspect of the present invention, said load circuit has a first load transistor and a second load transistor that have their gate terminals connected to each other and have their drain terminals connected to the drain terminals of said first transistor and said second transistor, respectively; it has an output exchange circuit which causes the drain terminals and gate terminals of said first load transistor and second load transistor to be connected to each other or disconnected from each other.
According to an aspect of the present invention, said reference voltage and said detection voltage input to said first input transistor and said second input transistor are swapped at least once per 1/60 sec under the control of said exchange controller.
In addition, the backlight device of the present invention may have a brightness adjusting switch, which is arranged between said amplifier and the gate terminal of said driving transistor, and which switches the connection state between said amplifier and said driving transistor ON/OFF, and a brightness controller, which controls the operation of said brightness adjusting switch; said exchange controller is constituted such that said detection voltage and said reference voltage input to said first input transistor and second input transistor are swapped during the period when the connection between said amplifier and said driving transistor is turned OFF.
According to an aspect of the present invention a type of light-emitting element driver is provided which driver serves to drive the light-emitting element for backlighting a display, and it has the following parts: a transistor, which is coupled to the current path of the light-emitting element and controls power ON for the light-emitting element, a detector, which is coupled to the current path of the light-emitting element and detects the current flowing in the light-emitting element, a driving signal generator, into which the detection voltage generated by said detector and a reference voltage are input, and which generates a driving signal for driving said transistor, and a switching circuit, which is coupled between said driving signal generator and said transistor, and which selectively feeds said driving signal to the control terminal of said transistor; said driving signal generator has the following parts: a first input terminal and a second input terminal, an output terminal, a differential circuit containing a first transistor and a second transistor, a load circuit coupled to said differential circuit, a first switching circuit containing a first switch that causes the control terminal of said first transistor to be connected to said first input terminal or said second input terminal, and a second switch that causes the control terminal of said second transistor to be connected to said second input terminal or said first input terminal, and a second switching circuit containing a third switch that receives the output signal fed from the first node or second node between said differential circuit and said load circuit, and sends it to said output terminal; the connection states of said first switch, second switch and third switch are switched during OFF period of the light-emitting element.
According to an aspect of the present invention, each period comprising the ON/OFF periods of the light-emitting element is synchronized with the horizontal synchronization signal or vertical synchronization signal of the display control signal.